DCN December 2016 - Page 32

cooling STEPPED BENEFITS Martin Passingham of Daikin UK explores the unique environment required by server rooms and telecom shelters, and the benefits of a two-step cooling system design. U nlike a standard living environment such as a home or office, infrastructure cooling requires a constant, specific set of climatic conditions to ensure downtime is minimalised. Any unexpected or planned interruptions not only incur unplanned business costs but also impact upon the service provided to customers, who rely on consistent access to their data connections. Understanding and maintaining the specific climatic requirements of a server room or telecom shelter is essential. In a typical residential 32 or commercial property, humidity is present and the temperature control capacity is balanced. However, in an infrastructure cooling environment, there is limited or no humidity due to the vast number of computers, servers and other technologies generating minimal moisture. This is beneficial for the unique environment as high humidity can lead to condensation, which can cause corrosion or, in extreme circumstances, electrical shorts. On the other end of the spectrum, too little humidity can promote a build up of electrostatic charge that can destroy sensitive electronics.  Therefore, the relative humidity (RH) within the centre should be less than 30 per cent and the temperature set at 20-22°C. This then provides the ideal atmospheric conditions for the computers within the centre to operate. When considering installing an air conditioning system, for normal cooling applications a combination of indoor and outdoor units with matching capacities are traditionally used. This is due to the indoor unit having the ability, and additional cooling capacity, to withstand the higher humidity conditions and varying temperature requirements associated with a living environment. Applying this logic to an infrastructure cooling environment can, however, have detrimental consequences, comprising reliability and resulting in frequent downtimes. Asymmetric system Due to the need to extract heat energy from dry air, the indoor unit needs enhanced cooling capabilities for continuous heat transfer. Therefore an asymmetric system is recommended. An asymmetric air conditioning combination pairs a larger capacity indoor unit with a small outdoor unit, for example, a 71 class exterior unit and a 100 class indoor unit. A twostep system design process takes into account all influencing factors, as well as back up plans should a unit fail. When approaching the system design, step one determines the indoor conditions and the required cooling demand. Step two then enables a suitable system combination to be selected from a unit combination table, providing a bespoke solution that ensures the appropriate capacity is available to meet the indoor cooling demand. Pairing a larger indoor unit with a smaller exterior air conditioning unit presents several unique benefits. For example, the asymmetric combination provides a 20-40 per cent increase